This program of research attempts to identify regions of the central visual system involved in visual attention and visual pattern discrimination in cats and monkeys. Particular emphasis is placed upon the pulvinar and the regions of the cortex to which it projects, including inferotemporal and extrastriate cortex. Five major areas of investigation are outlined: 1. Identification of the sources and nature of functional visual input to the pulvinar, 2. Determination of the interrelationships and interactions of the pulvinar with visual and association cortex, 3. Use of the pulvinar as a model system for conditioning of single unit responses, 4. Role of the pulvinar and inferotemporal cortex in visual attention and visual pattern discrimination learning associated with eye movements, fixations and visual tracking behavior. Methods include electrophysiological recording (single unit and average evoked potentials), electrical stimulation, reversible cryogenic blockade, electrolytic lesions, and behavioral training techniques designed to seperate attentional and visual discriminative processes. Projects 1 and 2 investigate the tecto-pulvinar-cortical visual system in cats; project 3 investigates neuronal plasticity in the pulvinar of cats by attempted auditory conditioning of single visual units; project 4 attempts to distinguish deficits in visual memory, visual attention and visual discrimination in nemestrina monkeys by local cryogenic blockade or lesions of the pulvinar and inferotemporal cortex, project 5 utilizes combined electrophysiological and behavioral methods in squirrel monkeys to determine the role of eye movements in attention and perception. These studies of the role of the pulvinar and its cortical projections in visual attention and perception also have relevance for understanding some of the disorders attributed to the pulvinar and its cortical projections, such as reading, writing and speech disabilities, and deficits in perceptual and higher cognitive functions. BIBLIOGRAPHIC REFERENCES: Chalupa, L. M., Macadar, A. W. and Lindsley, D. B. Response plasticity of lateral geniculate neurons during and after pairing of auditory and visual stimuli. Science, 1975, 190, 290-292. Chalupa, L. M., Rohrbaugh, J. W., Gould, J. E. and Lindsley, D. B. Cortical and subcortical visual evoked potential correlates of reaction time in monkeys. J. comp. physiol. Psychol., 1976, 8, 119-126.